A typical data storage system includes a magnetic medium for storing data in magnetic form and a transducer used to read and/or write magnetic data from/to the storage medium. A disk storage device, for example, includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute. Digital information, representing various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to an actuator assembly and passed over the surface of the rapidly rotating disks.
The actuator assembly typically includes a coil assembly and a plurality of outwardly extending arms having flexible suspensions with one or more transducers and slider bodies being mounted on the suspensions. The suspensions are interleaved within the stack of rotating disks, typically by means of an arm assembly (E/Block) mounted to the actuator assembly. The coil assembly generally interacts with a permanent magnet structure, and is responsive to a controller. A voice coil motor (VCM) is also mounted to the actuator assembly diametrically opposite the actuator arms.
In a typical digital data storage system, digital data is stored in the form of magnetic transitions on a series of concentric, spaced tracks comprising the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors, with each sector comprising a number of information fields. One of the information fields is typically designated for storing data, while other fields contain track and sector position identifications and synchronization information, for example. Data is transferred to, and retrieved from, specified track and sector locations by the transducers which follow a given track and move from track to track, typically under the servo control of a controller.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the transducer assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element passes over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface results in the production of electrical signals in the read element. The electrical signals correspond to transitions in the magnetic field.
Conventional data storage systems generally employ a closed-loop servo control system for positioning the actuator and read/write transducers to specified storage locations on the data storage disk. During normal data storage system operation, a servo transducer, generally mounted proximate the read/write transducers, or, alternatively, incorporated as the read element of the transducer, is typically employed to read information for the purpose of following a specified track (track following) and seeking specified track and data sector locations on the disk (track seeking).
A servo track writing procedure is typically implemented to initially record servo pattern information on the surface of one or more of the data storage disks. A servo track writer (STW) assembly is typically used by manufacturers of data storage systems to facilitate the transfer of servo pattern data to one or more data storage disks during the manufacturing process.
In accordance with one known STW technique, embedded servo pattern information is written to the disk along segments extending in a direction generally outward from the center of the disk. The embedded servo pattern is thus formed between the data storing sectors of each track. It is noted that a servo sector typically contains a pattern of data, often termed a servo burst pattern, used to maintain optimum alignment of the read/write transducers over the centerline of a track when reading and writing data to specified data sectors on the track. The servo information may also include sector and track identification codes which are used to identify the position of the transducer.
The servo burst pattern typically induces signals in the read element (readback signals) which are used to develop a position error signal (PES signal). The PES signal is used to maintain the transducer over the centerline of the track. An offset in the PES signal generally causes a servo system to position the transducer offtrack (i.e., spaced from the centerline of a track). If offsets in a PES signal change over time, deleterious write-to-write track misregistration and write-to-read track misregistration can occur. For example, when a track is written using a PES signal with no offset and later read with an offset PES signal, there may be errors in the information read. Similarly, when a track is written using a PES signal with no offset and an adjacent track is written with an offset PES signal, there may be errors in the information written to the tracks.